Introduce EntityRetrievingClosestReferencedEntityIdLookup

src/Lookup/EntityRetrievingClosestReferencedEntityIdLookup.php

@@ -0,0 +1,249 @@
+<?php
+
+namespace Wikibase\DataModel\Services\Lookup;
+
+use Wikibase\DataModel\Entity\EntityId;
+use Wikibase\DataModel\Entity\EntityIdValue;
+use Wikibase\DataModel\Entity\PropertyId;
+use Wikibase\DataModel\Services\Entity\EntityPrefetcher;
+use Wikibase\DataModel\Snak\PropertyValueSnak;
+use Wikibase\DataModel\Snak\Snak;
+use Wikibase\DataModel\Statement\StatementListProvider;
+
+/**
+ * Service for getting the closest entity (out of a specified set),
+ * from a given starting entity. The starting entity, and the target entities
+ * are (potentially indirectly, via intermediate entities) linked by statements
+ * with a given property ID, pointing from the starting entity to one of the
+ * target entities.
+ *
+ * @since 3.10
+ *
+ * @license GPL-2.0-or-later
+ * @author Marius Hoch
+ */
+class EntityRetrievingClosestReferencedEntityIdLookup implements ReferencedEntityIdLookup {
+
+	/**
+	 * @var EntityLookup
+	 */
+	private $entityLookup;
+
+	/**
+	 * @var EntityPrefetcher
+	 */
+	private $entityPrefetcher;
+
+	/**
+	 * @var int Maximum search depth: Maximum number of intermediate entities to search through.
+	 *  For example 0 means that only the entities immediately referenced will be found.
+	 */
+	private $maxDepth;
+
+	/**
+	 * @var int Maximum number of entities to retrieve.
+	 */
+	private $maxEntityVisits;
+
+	/**
+	 * Map (entity id => true) of already visited entities.
+	 *
+	 * @var bool[]
+	 */
+	private $alreadyVisited = [];
+
+	/**
+	 * @param EntityLookup $entityLookup
+	 * @param EntityPrefetcher $entityPrefetcher
+	 * @param int $maxDepth Maximum search depth: Maximum number of intermediate entities to search through.
+	 *  For example if 0 is given, only the entities immediately referenced will be found.
+	 *  If this limit gets exhausted, a MaxReferenceDepthExhaustedException is thrown.
+	 * @param int $maxEntityVisits Maximum number of entities to retrieve during a lookup.
+	 *  If this limit gets exhausted, a MaxReferencedEntityVisitsExhaustedException is thrown.
+	 */
+	public function __construct(
+		EntityLookup $entityLookup,
+		EntityPrefetcher $entityPrefetcher,
+		$maxDepth,
+		$maxEntityVisits
+	) {
+		$this->entityLookup = $entityLookup;
+		$this->entityPrefetcher = $entityPrefetcher;
+		$this->maxDepth = $maxDepth;
+		$this->maxEntityVisits = $maxEntityVisits;
+	}
+
+	/**
+	 * Get the closest entity (out of $toIds), from a given entity. The starting entity, and
+	 * the target entities are (potentially indirectly, via intermediate entities) linked by
+	 * statements with the given property ID, pointing from the starting entity to one of the
+	 * target entities.
+	 *
+	 * @since 3.10
+	 *
+	 * @param EntityId $fromId
+	 * @param PropertyId $propertyId
+	 * @param EntityId[] $toIds
+	 *
+	 * @return EntityId|null Returns null in case none of the target entities are referenced.
+	 * @throws ReferencedEntityIdLookupException
+	 */
+	public function getReferencedEntityId( EntityId $fromId, PropertyId $propertyId, array $toIds ) {
+		if ( !$toIds ) {
+			return null;
+		}
+
+		$this->alreadyVisited = [];
+
+		$steps = $this->maxDepth + 1; // Add one as checking $fromId already is a step
+		$toVisit = [ $fromId ];
+
+		while ( $steps-- ) {
+			$this->entityPrefetcher->prefetch( $toVisit );
+			$toVisitNext = [];
+
+			foreach ( $toVisit as $curId ) {
+				$result = $this->processEntityById( $curId, $fromId, $propertyId, $toIds, $toVisitNext );
+				if ( $result ) {
+					return $result;
+				}
+			}
+			// Remove already visited entities
+			$toVisit = array_unique(
+				array_diff( $toVisitNext, array_keys( $this->alreadyVisited ) )
+			);
+
+			if ( !$toVisit ) {
+				return null;
+			}
+		}
+
+		// Exhausted the max. depth without finding anything.
+		throw new MaxReferenceDepthExhaustedException(
+			$fromId,
+			$propertyId,
+			$toIds,
+			$this->maxDepth
+		);
+	}
+
+	/**
+	 * Find out whether an entity (directly) references one of the target ids.
+	 *
+	 * @param EntityId $id Id of the entity to process
+	 * @param EntityId $fromId Id this lookup started from
+	 * @param PropertyId $propertyId
+	 * @param EntityId[] $toIds
+	 * @param EntityId[] &$toVisit List of entities that still need to be checked
+	 * @return EntityId|null Target id the entity refers to, null if none.
+	 */
+	private function processEntityById(
+		EntityId $id,
+		EntityId $fromId,
+		PropertyId $propertyId,
+		array $toIds,
+		array &$toVisit
+	) {
+		$entity = $this->getEntity( $id, $fromId, $propertyId, $toIds );
+		if ( !$entity ) {
+			return null;
+		}
+
+		$mainSnaks = $this->getMainSnaks( $entity, $propertyId );
+
+		foreach ( $mainSnaks as $mainSnak ) {
+			$result = $this->processSnak( $mainSnak, $toVisit, $toIds );
+			if ( $result ) {
+				return $result;
+			}
+		}
+
+		return null;
+	}
+
+	/**
+	 * @param EntityId $id Id of the entity to get
+	 * @param EntityId $fromId Id this lookup started from
+	 * @param PropertyId $propertyId
+	 * @param EntityId[] $toIds
+	 *
+	 * @return StatementListProvider|null Null if not applicable.
+	 */
+	private function getEntity( EntityId $id, EntityId $fromId, PropertyId $propertyId, array $toIds ) {
+		if ( isset( $this->alreadyVisited[$id->getSerialization()] ) ) {
+			trigger_error(
+				'Entity ' . $id->getSerialization() . ' already visited.',
+				E_USER_WARNING
+			);
+
+			return null;
+		}
+
+		$this->alreadyVisited[$id->getSerialization()] = true;
+
+		if ( count( $this->alreadyVisited ) > $this->maxEntityVisits ) {
+			throw new MaxReferencedEntityVisitsExhaustedException(
+				$fromId,
+				$propertyId,
+				$toIds,
+				$this->maxEntityVisits
+			);
+		}
+
+		try {
+			$entity = $this->entityLookup->getEntity( $id );
+		} catch ( EntityLookupException $ex ) {
+			throw new ReferencedEntityIdLookupException( $fromId, $propertyId, $toIds, null, $ex );
+		}
+
+		if ( !( $entity instanceof StatementListProvider ) ) {
+			return null;
+		}
+
+		return $entity;
+	}
+
+	/**
+	 * Decide whether a single Snak is pointing to one of the target ids.
+	 *
+	 * @param Snak $snak
+	 * @param EntityId[] &$toVisit List of entities that still need to be checked
+	 * @param EntityId[] $toIds
+	 * @return EntityId|null Target id the Snak refers to, null if none.
+	 */
+	private function processSnak( Snak $snak, array &$toVisit, array $toIds ) {
+		if ( ! ( $snak instanceof PropertyValueSnak ) ) {
+			return null;
+		}
+		$dataValue = $snak->getDataValue();
+		if ( ! ( $dataValue instanceof EntityIdValue ) ) {
+			return null;
+		}
+
+		$entityId = $dataValue->getEntityId();
+		if ( in_array( $entityId, $toIds, false ) ) {
+			return $entityId;
+		}
+
+		$toVisit[] = $entityId;
+
+		return null;
+	}
+
+	/**
+	 * @param StatementListProvider $statementListProvider
+	 * @param PropertyId $propertyId
+	 * @return Snak[]
+	 */
+	private function getMainSnaks(
+		StatementListProvider $statementListProvider,
+		PropertyId $propertyId
+	) {
+		return $statementListProvider
+			->getStatements()
+			->getByPropertyId( $propertyId )
+			->getBestStatements()
+			->getMainSnaks();
+	}
+
+}

src/Lookup/MaxReferenceDepthExhaustedException.php

@@ -0,0 +1,51 @@
+<?php
+
+namespace Wikibase\DataModel\Services\Lookup;
+
+use Exception;
+use Wikibase\DataModel\Entity\EntityId;
+use Wikibase\DataModel\Entity\PropertyId;
+
+/**
+ * @since 3.10
+ *
+ * @license GPL-2.0-or-later
+ * @author Marius Hoch
+ */
+class MaxReferenceDepthExhaustedException extends ReferencedEntityIdLookupException {
+
+	/**
+	 * @var int
+	 */
+	private $maxDepth;
+
+	/**
+	 * @param EntityId $fromId
+	 * @param PropertyId $propertyId
+	 * @param EntityId[] $toIds
+	 * @param int $maxDepth
+	 * @param string|null $message
+	 * @param Exception|null $previous
+	 */
+	public function __construct(
+		EntityId $fromId,
+		PropertyId $propertyId,
+		array $toIds,
+		$maxDepth,
+		$message = null,
+		Exception $previous = null
+	) {
+		$this->maxDepth = $maxDepth;
+		$message = $message ?: 'Referenced entity id lookup failed: Maximum depth of ' . $maxDepth . ' exhausted.';
+
+		parent::__construct( $fromId, $propertyId, $toIds, $message, $previous );
+	}
+
+	/**
+	 * @return int
+	 */
+	public function getMaxDepth() {
+		return $this->maxDepth;
+	}
+
+}

src/Lookup/MaxReferencedEntityVisitsExhaustedException.php

@@ -0,0 +1,52 @@
+<?php
+
+namespace Wikibase\DataModel\Services\Lookup;
+
+use Exception;
+use Wikibase\DataModel\Entity\EntityId;
+use Wikibase\DataModel\Entity\PropertyId;
+
+/**
+ * @since 3.10
+ *
+ * @license GPL-2.0-or-later
+ * @author Marius Hoch
+ */
+class MaxReferencedEntityVisitsExhaustedException extends ReferencedEntityIdLookupException {
+
+	/**
+	 * @var int
+	 */
+	private $maxEntityVisits;
+
+	/**
+	 * @param EntityId $fromId
+	 * @param PropertyId $propertyId
+	 * @param EntityId[] $toIds
+	 * @param int $maxEntityVisits
+	 * @param string|null $message
+	 * @param Exception|null $previous
+	 */
+	public function __construct(
+		EntityId $fromId,
+		PropertyId $propertyId,
+		array $toIds,
+		$maxEntityVisits,
+		$message = null,
+		Exception $previous = null
+	) {
+		$this->maxEntityVisits = $maxEntityVisits;
+		$message = $message ?: 'Referenced entity id lookup failed: Maximum number of entity visits (' .
+				$maxEntityVisits . ') exhausted.';
+
+		parent::__construct( $fromId, $propertyId, $toIds, $message, $previous );
+	}
+
+	/**
+	 * @return int
+	 */
+	public function getMaxEntityVisits() {
+		return $this->maxEntityVisits;
+	}
+
+}